In wide area wireless communication networks, relatively high power base station devices are provided to serve wireless client devices or user devices. Each base station device is capable of serving wireless user devices in a coverage area that is primarily determined by the power of the signal it can transmit. Wireless service to user devices located within large buildings becomes degraded because the user device has difficulty receiving a signal from the base station, even if the building is well within the coverage area of the base station.
To augment the coverage of the wireless network, wireless transceiver devices with relatively small coverage areas (and serving capacities) are deployed. Depending on their coverage area and serving capacities, these wireless transceiver devices are referred to as “femto” cells or “pico” cells, or more generally, small cell access point devices. For simplicity and generality, the term radio access point (RAP) device is used herein to refer to a wireless transceiver device that is configured to serve wireless user devices over relatively small coverage areas and with generally less capacity as compared to a macro base station that is configured to serve a relatively large coverage area (“macro cell”) and consequently many more client devices. The RAP devices may be deployed inside or near buildings to serve client devices where signals from a macro base station are too weak.
The client device and RAP devices use a frequency and primary scrambling code combination. The frequency identifies the radio frequency channel in the wireless spectrum that is used for communication with the client device. The primary scrambling code is used to distinguish one cell (macro cell or RAP cell) from another that uses the same frequency. In certain scenarios, it is possible for two RAPs that are not within radio range of each other, to use the same primary scrambling code. Although the RAPs are not within radio range of each other, both RAPs may be visible to the client device. When this occurs, the client device can receive signals from both RAPs that interfere with each other. The interference may result in garbled reception or dropped service for the client device.